Field of the Invention
This invention relates to articles having relatively movable parts and, more particularly, to a system incorporated into such an article to guide relative movement between those parts.
Background Art
A multitude of articles, in many different fields, incorporate parts that are movable relative to each other to reconfigure the article to change how the article performs, is shaped, and/or interacts with a user. One example of such an article is an adjustable desk chair having a seat, back rest, and armrest.
Designers of desk chairs often strive to come up with a “one size fits all” version. At the same time, users of these chairs have come to expect a high degree of adjustability, to include changing the heights of the seat, back rest, and armrests, and changing the angular relationship between the seat and back rest. Ideally, the component parts of such chairs would move to precisely follow specific torso and limb movements as the user changes positions while remaining seated.
Most commonly, the mechanisms that are utilized for the above purpose are those that permit translational movement between the parts and those that permit pivoting movement of the parts, one relative to the other. For example, back rests are commonly pivoted relative to a supporting frame/base about a horizontal, laterally extending axis between upright and reclined positions. Armrests are typically made to translate in a vertical line relative to the supporting frame to which the seat and back rest are mounted. While these mechanisms and conventional designs permit some reasonable degree of conformity to typical body movements, they are in many respects deficient.
For example, the above-described armrests typically are of limited use to, and may even be uncomfortable for, a reclined user. That is, while the upwardly facing support surface on each armrest does remain accessible, conventional adjustment mechanisms do not allow the armrest to reposition so as to conformingly support a reclined user's arm that may be turned in multiple directions as permitted through the elbow and shoulder joints. For example, a reclined user attempting to hold a book, magazine, or electronic device in a raised position typically will get limited benefit from the armrest only by leaning his/her elbow or upper arm region on the edge of the arm support. This leaves the forearm region virtually unsupported which may lead to rapid fatigue.
With respect to the back rest, typically, the horizontal pivot axis will be at a location spaced from the region at the lower region of a user's back where the upper and lower parts of the body naturally hinge. As a result, as a user moves between reclined and upright positions, the user's back will slide relative to the back rest. The user's back thus is in different relationships with the back rest as he/she hinges his/her upper body. When this occurs, the user must either make a compensating movement once the desired back rest angle is achieved, or settle for a less than optimal relationship between the user's back and head and the back rest. This might be particularly a problem when back rests are designed for a specific and consistent relationship between a user's head and back.
Additional conformity problems are introduced when the seat incorporates an angular adjustment capability independently of the back rest or somehow in synchronization therewith. Aside from the inconvenience of having to adjust and shift, the user faces the possibility that no relationship between the seat and back rest will be achievable that allows comfortable conformity to a user with his/her body in different states.
Many of the above limitations with conventional mechanisms are experienced with other categories of articles with relatively movable parts. This includes articles that are not required to conform to human anatomy but require strategic relative movement between parts.
For example, complicated mechanisms are often incorporated to allow tables to be collapsed. Leg assemblies are integrated into table tops so that the legs generally pivot around a fixed axis with control and stability afforded by pivotably connected linkage parts.
Some designs for relatively movable parts incorporate ball-and-socket arrangements which allow universal relative movement between parts. Ball-and-socket connections, while effective in allowing universal movement between two parts, have a number of drawbacks.
First of all, the forces exerted on the surfaces cooperating between ball-and-socket components may be very substantial, particularly when the components themselves are heavy and/or there is significant loading on one or more of the relatively movable parts in use. To maintain stability for this type of article, it may be necessary to make parts with high load capacity, which may add to the design complication, expense, and unwanted weight. This type of design also may be prone to excessive wear, given the concentration of forces between the engaging surfaces on components between which there is relative movement. As a result, ongoing maintenance, such as lubrication, may be required. Alternatively, parts may have to be periodically changed as they wear and become less easily operable or wear to the point that alignment is altered or there is a malfunction.
Further, with a ball-and-socket type arrangement, it is generally difficult to lock the cooperating components together to avoid relative movement between the associated parts, particularly when the parts are subjected to relatively large operating forces. Thus, there is a tendency of the parts to slip, which again leads to potential wear and parts failure. Alternatively, the parts can be made to be more robust, as described above, which can lead to added expense, size, and weight.
As a result, it is not practical in many applications for purveyors to offer articles with universal-type joints to permit the optimal relative movement between parts. Thus, the user generally is faced with options, each of which involves compromise on some level. For example, with existing adjustable furniture, users generally contend with linkages that are designed for durability yet which will not permit comfortable conformance to various torso and limb movements. Lighter-duty products with such universal adjustment capability are typically either undesirably expensive or made with the anticipation that they will be repaired or placed on a fairly regular basis.
Many industries, including the furniture industry, continue to seek out designs that accommodate relative movement between parts that are optimal in terms of permitted adjusting movements, affordability, and adequate life cycle.